Nickel alloy



United States Patent 3,093,518 NICKEL ALLOY Clarence G. Bieber, Roselle Park, NJ., assignor to The International Nickel Company, Inc., New York, NY, a corporation of Delaware No Drawing. Filed Sept. 11, 1959, Ser. No. 839,296 5 Claims. (Cl. 148-31) The present invention relates to alloys and, more particularly, to nickel-containing ferrous alloys adapted to be brought to high strength and hardness levels by means of appropriate heat treatment.

It is well known that carbon steels containing substantial amounts of carbon can be hardened to hardness levels in excess of about 50 Rockwell C (Re) (513 Vickers (V.H.N.) for example, up to about 65 Re (830 V.H.N.) and higher. Usually the very high hardnesses can be obtained only in very thin sections or near the surface of a thick section since alloying additions which permit deeper hardenabili-ty very often cause a reduction of the final hardness value obtainable. It is also well recognized that such steels have relatively poor corrosionresisting properties. On the other hand, chromium-containing and nickel-chrornium-containing steels of the austenitic type which have good corrosion-resistance characteristics are not normally capable of being hardened to such high hardness levels as represented by a value in the order of about 513 V.H.N. '01 higher. Chromium-containing stainless steels of the'martensitic type are also not usually capable of being hardened to such high hardness levels. A notable exception to this generalization are martensitic chromium-containing steels having a high carbon content. While these steels can be produced in a highly hardened condition, it is to be noted that under. these circumstances these steels exhibit almostno ductility and are incapable of being readily welded.

It has been a continuing object of metallurgical research to provide alloys which are capable of being hardened to very high levels of hardness uniformly or substantially uniformly throughout large sections, while at the same time retaining as much as possible of the corrosion-resisting characteristics exhibited by the so-called stainless or -rust-free steels. In addition to these two characteristics, the metallurgical art has sought to develop alloys which, in addition, exhibit high yield strength (Y.S.), high ultimate tensile strength (U.T.S.), good ductility and relatively good impact properties. Further, the alloys should be capable of retaining a high proportion of these characteristics when employed in environments wherein the temperature ranges from below room temperature up to the vicinity of about 1000" F. or higher. An additional requirement of practical alloys is a capability to be readily welded. Although attempts were made to provide such an alloy, none, as far as I am aware, was entirely successful when carried into practice commercially on an in dustrial scale.

It has now been discovered that by suitably proportioning the elements nickel and titanium (and/ or aluminum), in a low carbon, essentially chromiurnand nitrogen f-ree iron base, alloys can be provided which upon suitable heat treatment will exhibit a high combination of useful char: acteristics including hardness, corrosion resistance, yield strength, ultimate tensile strength, ductility, impact resistance, weldability, etc.

It is an object of the present invention to provide a novel ferrous-base alloy capable ofbeing heat treated to a high level of useful characteristics. 1 Another object of the invention is to provide a move heat treated ferrous-base alloy having a high level of useful characteristics.

The invention also contemplates providing a novel process for the production of an alloy having a high level of useful characteristics.

A further object of the invention is to provide a novel process for heat treating alloys.

Other objects and advantages will become apparent from the following description.

Generally speaking, the present invention contemplates alloys containing about 24% to about 30% nickel, about 1.5% to about 9% titanium and/ or aluminum, up to about 0.1% carbon, up to about 2% niobium, up to about 0.5% silicon, up to about 1.0% manganese, up to about 10% cobalt, up to about 0.10% calcium, up to about 0.1% boron, up to about 0.1% zirconium, up to about 0.25% vanadium with the balance being essentially iron including small amounts of other elements which do not adversely affect the novel characteristics of the alloy. Advantageously, when a combination of high ductility and high strength is required, titanium is present in the alloy in amounts of about 1% to 3%. Carbon is advantageously maintained below about 0.05% and more advantageously below about 0.03% and even below about 0.01%. When high ductilitycombined with high strength is re quired, niobium is advantageously present in the alloy in amounts at least about ten times the carbon content and up to 100 times the carbon content or higher. When the aluminum plus titanium content is low, e.g., about 3% or lower, it is normally advantageous to maintain the nickel content below about 28% Where maximum hardness, e.g., about 830 V.H.N. (65 R0) or higher is desired, it is most advantageous to have about 5% to about 9% of aluminum plus titanium in the alloy. Impurities such as sulfur, phosphorus, nitrogen, etc., should be maintained at the lowest levels which are practical. Advantageously, the total amount of these impurities should be not in excess of about 0.05% and should, if possible, be even lower. Advantageously, chromium and/or molybdenum should not be present in the alloys and, in any event, chromiumand/or molybdenum should not be present in amounts greater than about 2% total when it is desired to obtain the best combination of maximum hardness and ductility.- If desired, the cobalt content of the alloys can be as high as 20%.

When the aforementioned ranges of composition are maintained, the alloys can be hot worked at temperatures in excess of about 1400 F. and, more particularly, within the range. of about 1400 F. to about 2150 F. or even higher. These alloys can also be readily cold worked provided the metal is cooled rapidly from a solution treating temperature of about 1400 F. to about 1800" F. It is to be noted that the alloys can be hardened by cold working and this hardening can be supplemented by heat treatment as disclosed hereinafter. If it is not necessary for the alloy to be amenable to softening to 'facilitate cold Working operations, the nickel content can be decreased. For-example, the nickel content can be as low as 20% or even 18% in alloys which do not require substantial amounts of cold working. I

In accordance with the present invention, the afore mentioned alloys which contain about 18% to about 30% nickel can be heat treated from the solution treated condition produced by heating the alloy at temperatures in the range of about 1400 F. to about 2150 F. for 025 hour or longer, e.g., one hour, by subjecting them to a first aging treatment for a period of from 1 to 24 hours at a temperature above the mar-tensitic transformation range and within the range of from about 1100 F. to about 1400 F.; cooling the alloys to a temperature at least below F. to effect a transformation and conducting a second aging treatment at a temperature below about 1200 F., for example, within the range of about 500 F. to about 1200 F., for a period of about A to about 24 hours. Advantageously, about 1000 F. can be employed as the maximum temperature in the second aging step. With regard to the heat treatment, it is usually advantageous to employ longer aging times in association with lower temperatures and vice versa during each step. With alloys having nickel contents near the lower end of the range, for example, about 18% to about 23% nickel, it is sometimes advantageous to omit the first aging step after solution treatment. Further, with respect to all of the alloys of the present invention, the cooling step can be varied with respect to both time and temperature. Thus, the alloys can be refrigerated for several hours or can be permitted to remain at room temperature for a period of time ranging from a few minutes to several days.

It is to be noted that by varying the particular stages of heat treatment, a wide variety of combinations of physical characteristics can be produced in the alloys. This fact is considered highly advantageous since by judicious selection of particular heat treatment conditions, a single alloy can be tailor made to fit any one of a number of difierent end uses. For example, one alloy can have uniform hardness characteristics in sections of up to 24 inches thick and even thicker with the hardness ranging in different specimens from 42 Re up to 5 8 Re, i.e., from about 412 to about 655 V.H.N. Other alloys have been made which have hardnesses up to at least about 67 Re (900 V.H.N.). When alloys in accordance with the present invention containing greater than about 24% nickel are quenched from the solution treated condition, hardnesses of between about 4 and about 15 Rc are commonly exhibited. For example, alloys which in the solution treated condition exhibit hardnesses of the order of about 150 V.H.N. Rc), can be hardened to levels in excess of about 513 V.H.N. (50 Rc) and even up to 830 V.H.N. (65 Rc) and higher. Other physical characteristics are equally controllable. These alloys exhibit very low yield strengths in the solution treated condition and thus can be readily worked. When hardened, the alloys exhibit yield strengths in the range of about 150,000 pounds per square inch (p.s.i.) up to about 290,000 p.s.i. or even higher. Ultimate tensile strengths of the hardened alloys can be as high as 305,000 psi. and even higher. In addition to the flexibility of the alloys of the present invention with respect to mechanical characteristics, the alloys also exhibit advantageous oxidationand corrosion resistance when compared to carbon steels which can be hardened by a dilferent mechanism to hardness levels of similar magnitude.

For the purpose of giving those skilled in the art a better understanding of the invention, some alloys in accordance with the present invention are set forth in Table I:

Including minute amounts of unavoidable impurities and residual amounts of deoxidizer.

Alloys Nos. 2 and represent those alloys within the present invention which exhibit good all around physical characteristics including high hardness, high yield strength, high ultimate tensile strength and acceptable ductility in the heat treated, fully aged condition. In the solution treated condition, these alloys are soft and readily workable both by hot working and cold Working techniques. Alloy No. 3 is illustrative of those alloys of the present invention which can be hardened to extremely high levels uniformly through large sections and which, in the solution treated condition, exhibit good workability and low hardness. Alloys Nos. 1, 4, 6 and 7 are representative of those alloys of the present invention which at hardness levels in excess of about 50 Re exhibit a good combination of yield strength, ultimate tensile strength and ductility, but which are not readily produced in a soft condition after solution treatment.

As mentioned hereinbefore, the alloys of the present invention can be hardened by heat treatment to produce high hardness values. Some specific hardening treatments in accordance with the present invention which are advantageously employed after the alloy has been subjected to a solution treatment by maintaining it at a temperature of about 1450 F. to about 1600 F. for a period of about 0.25 hour to about 4 hours, e.g., about 1 hour, are set iiorth in Table II:

Table II 1st Aging Cooling 2nd Aging Heat Treatment Hours Temp., Hours Temp., Hours Temp.,

F. F. F.

l, 300 16 1 950 1,300 0001 to room 1 950 temperature 1, 300 16 100 4 850 1, 10 100 1 950 1, 200 8 0 1 950 1, 300 16 100 1 950 16 100 1 1, 050 16 -100 4 900 16 100 4 1, 000

It is to be noted with regard to Table II that when it is indicated that the alloy is refrigerated, for example, held for 16 hours at -100 F., the alloy is first cooled from the aging temperature to room temperature in some convenient medium, for example, cooled in air, in water, in oil, in furnace atmosphere, etc.

With regard to alloys of the present invention which are adapted to be produced in the soft condition, it is generally advantageous to cool the alloy after solution treatment to a temperature at least below about 1000" F. at a rate of the order of about 10 'F. per second when a high yield strength of the order of about 250,000 p.s.i. iOEl higher in the fully heat treated condition is desirable.

Examples of the physical characteristics obtainable with the alloys in accordance with the present invention as hardened also in accordance therewith are set forth in Tables III, IV, V and VI:

Table III Alloy Solution Heat Hardness Hardness No. Temp., F. Treatment as Solution as Aged,

Treated, Re Re 1, 600 C 18 58. 5 1, 900 E 6 66 1, 500 A 54 1, 600 B 54 1, 800 D 13 51 With respect to the data set forth in Table III, it is to be noted in particular that alloy No. 3 exhibited a low hardness as solution treated and an extremely high hardness after being aged. Reheating for an additional hour at 950 F. results in the alloy achieving an even greater hardness of 67 Re which is substantially uniform throughout any size section.

Some examples of tensile data obtained with alloys which can be solution treated to produce very soft ialloys are set forth in Table IV:

. Table IV Heat Elonga- Reduc- Alloy N 0. Treat- 0.2% Y.S. U.T.S. tlon, Pertion in ment (p.s.i.) (p.s.i.) cent Area (Percent) Tensile data obtained on alloys which cannot be readily softened by solution treatment are set fiorth in Table V:

It is to be noted that examples of alloys of the present invention exhibited high 0.2% yield strengths of the order of about 250,000 p.s.i. to about 290,000 p.s.i. or higher in the aged condition. Another alloy of the present invention containing about 20% nickel and about 3% aluminum plus titanium exhibited in the aged condition a yield strength of about 292,000 p.s.i. and an ultimate tensile strength of about 305,000 p.s.i. with Jan elongation of 6% and a reduction in area of about 22%. When very high 0.2% yield strengths of the order of about 250,000 p.s.i. or higher combined with relatively high ductility in the aged condition are desired, it is advantageous to solution treat the alloy near the low end of the solution treatment range, for example, at a temperature of about 1500 -F. or lower. The physical characteristics exhibited by the alloys of the present invention in the solution treated condition are exemplified by the doll-owing data. Alloy No. 2 referred to hereinbefore in Table I, was solution treated for one hour at 1500 F. and *air cooled. Under these conditions, the alloy had a hardness of 10 Re, an 0.2% yield strength of 50,300 p.s.i., an ultimate tensile strength of 113,700 p.s.i., an elongation of 35% and a reduction in area of 68.4%. When aged in accordance with heat treatment F, this same alloy exhibited :a U.T.S. of about 302,000 p.s.i. and an 0.2% Y.S. of about 266,000 p.s.i.

It is an advantageous characteristic of the present invention that in the hardened condition, the alloys do not undergo a brittle-ductile transformation. The data which are set forth in Table VI and which'clearly illustrate this point are the results of Charpy V notch tests conducted upon standard samples of alloy No. 4 which was hardened to a hardness of 51 Rc and which exhibited at this hardness level an 0.2% Y.S. of 249,000 p.s.i. and a U.T.S. of 261,200 p.s.i. with an elongation of -10% and a reduction in area of 45.3%. The samples were 10 mm. square, 55 in length containing a center 45 angle V notch 2 mm. deep with a bottom radius of 0.25 mm.

Table VI Energy (Foot Temperature Pounds) 1 R.T. is room temperature.

' An additional advantageous characteristic of the alloys of the present invention is that cooling rates scarcely affect the final hardness obtained. Samples of alloy No. 2 afiter having been subjected to a variety of solution treatments, first aging treatments and cooling treatments exhibited a final hardness between about 54 Rcand 58 R0 after a second aging for 1 hour at 950 F. regardless of whether the samples were water quenched, cooled in air or were slowly cooled in a furnace at a rate of about 100 F. per hour after the second aging treatment. A difierent situation prevails, however, with respect to hardness after solution treatment. As an example, a sample of alloy No. 2 solution treated at 1500 F. for one hour exhibited a hardness of 19 Re when quenched in water; a hardness of 15 Re when cooled in air and a hardness of 46 Rc when cooled slowly in a furnace at a rate of about 100 F. per hour. A lower solution temperature of 1400" F. produced a water quenched hardness of 35 Re and an air cooled hardness of 27 Rc. Conversely, a higher solution temperature of 18 00 F. resulted in a water quenched hardness of 7 R0 and an air cooled hard, ness of 3 Rc.

T The alloys 'of the present invention are particularly adapted to be formed into parts, structures, machines, etc., wherein a wide variety of metallurgical and physical characteristics are desired. Thus, alloys of the present invention can be employed as cutting tools, including knife edges, saws, lathe tools, files, high temperature bearings and bearing parts, forming tools, razor blades, forging dies, etc. The alloys of the present invention can also be employed in applications requiring high strength including pressure vessels, aircraft structural members, marine structural members, missile parts, skins and other members of supersonic aircraft, armor plate, armor piercing projectiles, etc. Since the alloys of the present invention also retain a good combination of physical characteristics at moderately elevated temperatures, the alloys can be advantageously employed in structures subjected in use to elevated temperatures of the order of about up to 1000 F. Because of the excellent formability of the alloys in accordance with the present invention, structural forms such as wire, rod, tube, bar, sheet, plate, etc., can be employed wherever required. Because of the good resistance to thermal shock and to stress cracking these structural forms can be readily assembled by welding to any desired configuration. In addition, if desired the alloys can be produced in cast forms, for example, precision castings.

' Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and uariations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

I claim:

1. A hardened ferrous-base alloy containing about 24% to about 30% nickel, about 1.5% to about 9% of metal selected from the group consisting of aluminum and titanium and up to about 0. 1% carbon exhibiting a hardness in excess of at least about 50 Re, said hard ness being induced in said alloy [after solution treatment by first aging said alloy at a temperature above the martcnsi-tic transformation range and within the range of about 1100 F. to about 1400 F. for about 1 hour to about 24 hours, cooling said alloy to a temperature at least below about F. to effect a transformation therein and thereafter again aging said alloy at a temperature of about 500 F. to about 1200 F. for about A hour to about 24 hours.

2. A process of hardening ferrous-base alloys containing at least about 1.5% of metal selected from the group consisting of titanium and aluminum, not more than about 0.1% carbon and about 18% to about 30% nickel comprising first aging said alloy at a temperature above the martensitic transformation range and within the range of about 1100 F. to about 1400 F. for about 1 hour to about 24 hours, cooling said alloy to a temperature at least below about 90 F. to effect a transformation therein and thereafter again aging said alloy at a temperature of about 500 F. to about 1200 F. for about hour to about 24 hours.

3. A process as in claim 2 wherein prior to the first aging, the alloy is solution treated at a temperature of about 1400 F. to about 1600" F.

4. A process of hardening ferrous-base alloys containing at least about 1.5% of metal selected from the group consisting of titanium and aluminum, not more than about 0.1% carbon and about 24% to about 30% nickel comprising first aging said alloy at a temperature above the martensitic transformation range and within the range of about 1100 F. to about 1400 F. for about 1 hour to about 24 hours, cooling said alloy to a temperature at least below about 90 F. to effect a transformation therein and thereafter again aging said alloy at a temperature of about 500 F. to about 1200 F. Ior about hour to about 24 hours.

5. A martensitic iron-base alloy containing about 18% to about 24% nickel, 1.5% to about 3% of metal selected from the group consisting of titaniumv and aluminum and mixtures thereof, carbon in unavoidable amounts up to 0.05%, columbium in an amount of at least 10 times the carbon content and up to 2%, up to 1% manganese, less than about 0.5% silicon, up to about 10% cobalt, up to about 0.1% calcium, up to 0.1% boron, up to 0.1% zirconium, up to not more than 2% chromium, and the balance essentially iron, said martensitic alloy being characterized in the solution treated condition by good hot and cold workability and said martensitic alloy being further characterized when in the age hardened condition by high yield and tensile strengths and high hardness combined with good ductility and weldability.

References Cited in the file of this patent UNITED STATES PATENTS 1,947,274 Ruder Feb. 13, 1934 1,968,569 Ruder July 31, 1934 2,048,163 Pilling et a1. July 21, 1936 2,048,164 Pilling et a1. July 21, 1936 2,285,406 Bieber June 9-, 1942 2,708,159 Foley et a1. May 10, 1955 2,715,576 Payson et a1 Aug. 16, 1955 

1. A HARDENED FERROUS-BASE ALLOY CONTAINING ABOUT 24% TO ABOUT 30% NICKEL, ABOUT 1.5% TO ABOUT 9% OF METAL SELECTED FROM THE GROUP CONSISTING OF ALUMINU, A TITANIUM AND UP TO ABOUT 0.1% CARBON EXHIBITING A HARDNESS IN EXCESS OF AT LEAST ABOUT 50 RC, SAID HARDNESS BEING INDUCED IN SAID ALLOY AFTER SOLUTION TREATMENT BY FIRST AGING SAID ALLOY AT A TEMPERATURE ABOVE THE MARTENSITIC TRANSFORMATION RANGE AND WITHIN THE RANGE OF ABOUT 1100*F. TO ABOUT 1400*F. FOR ABOUT 1 HOUR TO ABOUT 24 HOURS, COOLING SAID ALLOY TO A TREMPERATURE AT LEAST BELOW ABOUT 90*F. TO EFFECT A TRANSFORMATION THEREIN AND TREATAFTER AGAIN AGING SAID ALLOY AT A TEMPERATURE OF ABOUT 500*F. TO ABOUT 1200*F. FOR ABOUT 1/4 HOUR TO ABOUT 24 HOURS. 